Technical Field
The embodiments herein generally relate to quantitative permeation testing for personal protective equipment (PPE) contact scenarios including quality controls and environmental controls, to measure permeation of contaminants through protective materials.
Description of the Related Art
Multiple methods exist for measuring permeation through protective equipment. According to the U.S. Army Test Operating Procedure (TOP), the method depends on the physical state of the contaminant, and the detection method. For liquid-contamination-vapor detection, the suggested method was the Aerosol Vapor Liquid Assessment Group (AVLAG) test cell. This apparatus uses a vapor detection scheme with an air sweep under the test swatch to gather the vapor of permeated contaminant. Detection may utilize MINICAMS® monitoring systems (available from OI Analytical, Texas, USA), sorbent tubes, or bubblers to collect the vapor. A schematic of the AVLAG cell 5, as described in the TOP, is shown in FIGS. 1A (sealed configuration) and 1B (unassembled configuration). This method permits time-resolved quantification of vapor breakthrough and environmental control. However, this method allows for the quantification of the vapor phase only, requires the use of flat swatches, and generally requires a cumbersome setup. Accordingly, this method requires a relatively significant investment in infrastructure for proper operation.
For liquid-contamination-liquid-detection, the TOP suggests using an expulsion method. A schematic of the expulsion test apparatus 10 is illustrated in FIG. 2. Here, 1 psi of pressure is applied to a contaminated swatch 14 with a 1 lb. stainless steel weight 12. Colorimetric detector paper (e.g. M8) 16 is used to determine breakthrough time. This method achieves low costs for setup and operation, time-resolved detection, application of realistic forces, and simplicity. However, this method requires bulk-liquid breakthrough for detection, and results in lack of environmental control and a lack of quantification when detector paper is used. Moreover, the TOP provides limited guidance on quantifying breakthrough using this method.
In 2007, a permeation program was initiated to examine the performance of personal protective equipment (PPE) against contaminants. Given the low volatility of the test compounds, the vapor detection method was deemed insufficient. Furthermore, the liquid-contamination-liquid-detection precludes quantification of breakthrough. Therefore, a hybrid method was devised to enable quantification of breakthrough in a contact scenario, with environmental control. This method uses a sorbent pad under the test swatch within an AVLAG cell, The swatch is contaminated in accordance with the TOP, and at a chosen time point, the swatch is removed from the cell, and the sorbent pad is extracted. The extractant is analyzed to quantify breakthrough. As part of the testing, a divinylbenzene (DVB) pad is characterized for extraction efficiency. However, this method produces a variable level of contact between the swatch and sorbent pad. This is exacerbated with non-flat swatches taken from fingers of gloves, or folded portions of protective suits. Furthermore, there is no practical method to apply relevant forces of contact. Finally, the use of the AVLAG makes this system cumbersome and each swatch is limited to a single time point.
The need for the contact scenario has been demonstrated toxicologically with rabbits during a separate study. The rabbit study used a latex swatch, known to be permeable to the nerve agent VX, as the swatch test material. The swatch was either in direct contact with the rabbit skin, or elevated by 1 cm off the skin. The elevated scenario represented a vapor only condition for exposure. The same conditions were used in both cases with regard to skin condition, contamination density, contact time, and test material. Data collected included onset of toxic signs, time-resolved acetyl cholinesterase (AChE) enzymatic activity level, and quantitation of regenerated VX in the skin and blood. All rabbits in the direct-contact scenario died, while no signs to mild signs were observed in the vapor-only rabbits. The exposure level is further supported by AChE activities. Furthermore, the level of agent measured in the skin was several orders of magnitude greater for the rabbits in the direct-contact configuration. Given that gloves and other personal protective equipment (PPE) are in direct contact with the skin, there was a need to develop additional testing techniques and systems that enables quantification in a direct contact configuration.